The present invention relates to calculators and more particularly to a calculator for quickly providing the helicopter hover performance capability of a particular helicopter.
One of the most important characteristics of a helicopter is its hover performance capability (the maximum gross weight at which hovering is possible), and it is unquestionably good practice for a pilot to calculate such capability while planning a flight to insure that the particular helicopter chosen is suitable for the mission and load required to be transported. Helicopters typically include instrumentation providing readouts of outside air temperature and outside pressure at the altitude of the aircraft (pressure altitude) which variables are necessary for calculation of the hover performance capability. In the situation where, during flight planning, the aircraft appears to be marginally suitable for its intended mission, the hover performance capability should be recalculated shortly prior to the portion of the flight during which hovering is necessary or desired.
Heretofore, assessment of the aircraft's power and the gross weight at which it could hover has been a cumbersome, time-consuming effort as it required reference to various charts or graphs in the helicopter operator's manual supplied with the aircraft. For example, to determine the military rating torque available for the AH-1G military helicopter, the pilot has been required to enter the pressure altitude scale of the military power available chart, move horizontally to the intersection of the temperature line (interpolating as necessary), and then project vertically to the torquemeter (torque pressure) scale. For aircraft manuals in which a torquemeter scale is not available on the power available chart, the pilot must also convert the power available into terms of torque. The next step in determining the maximum gross weight at which hovering is possible for the specific pressure altitude, temperature, and military power has been to enter the appropriate hover ceiling chart with pressure altitude, move horizontally to the intersection of the temperature line (again interpolating as necessary) and project vertically to the gross weight scale. In a tactical or emergency situation there might be insufficient time for the several references to the operator's manual causing the pilot to rely solely on judgment and past experience. It will be appreciated also that such manual graphic computation methods may render less than the desired accuracy.
Although the electronic calculator art has undergone rapid advancement, such calculators are typically either of the four function type particularily suited for personal use, or of the relatively sophisticated and expensive scientific type designed for calculations requiring advanced mathemathics. The four function calculator is not well suited for calculations of hover performance capability since the calculations require the use of certain constants which relate only to a particular airframe/engine combination thus requiring individual entry of these many constants.
The improved electronic calculator of the present invention is specifically adapted to provide a computation and readout of a helicopter's military power available and the gross weight the helicopter is capable of hovering, immediately upon entering into the calculator only the outside air temperature and the pressure altitude. The calculator is provided with a read only memory into which all of the general constants, specific aircraft constants and necessary calculations are preprogrammed and stored. The calculator also includes a microprocessor or processing means for performing the necessary calculations and for transfering information to a random access memory. A keyboard or input means provides the means for entering the outside air temperature and pressure altitude into the microprocessor and subsequently into the random access memory. The keyboard also is constructed to direct the calculator to commence calculating and to display the military power rating and the maximum gross hover weight on a display means. A clock in the calculator controls the sequence of events in the microprocessor.
It is therefore the main object of the invention to provide an inexpensive electronic calculator which is capable of immediately and accurately calculating and displaying the military power rating and the maximum gross hover weight of a particular helicopter with only the parameters of the outside air temperature and the pressure altitude being keyed into the calculator.